[PATCH 08/11] rust/block: Add driver module

[Kevin Wolf <kwolf@redhat.com>]

This adds a barebones module for a block driver interface. Because there
is no native QAPI support for Rust yet, opening images takes a few
unsafe functions to call into C visitor functions. This should be
cleaned up later.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
 rust/block/src/driver.rs | 190 +++++++++++++++++++++++++++++++++++++++
 rust/block/src/lib.rs    |   1 +
 2 files changed, 191 insertions(+)
 create mode 100644 rust/block/src/driver.rs

diff --git a/rust/block/src/driver.rs b/rust/block/src/driver.rs
new file mode 100644
index 0000000000..5c7c46bfa0
--- /dev/null
+++ b/rust/block/src/driver.rs
@@ -0,0 +1,190 @@
+// Copyright Red Hat Inc.
+// Author(s): Kevin Wolf <kwolf@redhat.com>
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+// All of this is unused until the first block driver is added
+#![allow(dead_code)]
+#![allow(unused_macros)]
+#![allow(unused_imports)]
+
+use crate::{IoBuffer, SizedIoBuffer};
+use qemu_api::bindings;
+use std::ffi::c_void;
+use std::io::{self, Error, ErrorKind};
+use std::mem::MaybeUninit;
+use std::ptr;
+
+/// A trait for writing block drivers.
+///
+/// Types that implement this trait can be registered as QEMU block drivers using the
+/// [`block_driver`] macro.
+pub trait BlockDriver {
+    /// The type that contains the block driver specific options for opening an image
+    type Options;
+
+    // TODO Native support for QAPI types and deserialization
+    unsafe fn parse_options(
+        v: &mut bindings::Visitor,
+        opts: &mut *mut Self::Options,
+        errp: *mut *mut bindings::Error,
+    );
+    unsafe fn free_options(opts: *mut Self::Options);
+    unsafe fn open(
+        bs: *mut bindings::BlockDriverState,
+        opts: &Self::Options,
+        errp: *mut *mut bindings::Error,
+    ) -> std::os::raw::c_int;
+
+    /// Returns the size of the image in bytes
+    fn size(&self) -> u64;
+}
+
+/// Represents the connection between a parent and its child node.
+///
+/// This is a wrapper around the `BdrvChild` type in C.
+pub struct BdrvChild {
+    child: *mut bindings::BdrvChild,
+}
+
+impl BdrvChild {
+    /// Creates a new child reference from a `BlockdevRef`.
+    pub unsafe fn new(
+        parent: *mut bindings::BlockDriverState,
+        bref: *mut bindings::BlockdevRef,
+        errp: *mut *mut bindings::Error,
+    ) -> Option<Self> {
+        unsafe {
+            let child_bs = bindings::bdrv_open_blockdev_ref_file(bref, parent, errp);
+            if child_bs.is_null() {
+                return None;
+            }
+
+            bindings::bdrv_graph_wrlock();
+            let child = bindings::bdrv_attach_child(
+                parent,
+                child_bs,
+                c"file".as_ptr(),
+                &bindings::child_of_bds as *const _,
+                bindings::BDRV_CHILD_IMAGE,
+                errp,
+            );
+            bindings::bdrv_graph_wrunlock();
+
+            if child.is_null() {
+                None
+            } else {
+                Some(BdrvChild { child })
+            }
+        }
+    }
+
+    /// Reads data from the child node into a linear byte buffer.
+    ///
+    /// # Safety
+    ///
+    /// `buf` must be a valid I/O buffer that can store at least `bytes` bytes.
+    pub async unsafe fn read_raw(&self, offset: u64, bytes: usize, buf: *mut u8) -> io::Result<()> {
+        let offset: i64 = offset
+            .try_into()
+            .map_err(|e| Error::new(ErrorKind::InvalidInput, e))?;
+        let bytes: i64 = bytes
+            .try_into()
+            .map_err(|e| Error::new(ErrorKind::InvalidInput, e))?;
+
+        let ret = unsafe { bindings::bdrv_pread(self.child, offset, bytes, buf as *mut c_void, 0) };
+        if ret < 0 {
+            Err(Error::from_raw_os_error(ret))
+        } else {
+            Ok(())
+        }
+    }
+
+    /// Reads data from the child node into a linear typed buffer.
+    pub async fn read<T: IoBuffer + ?Sized>(&self, offset: u64, buf: &mut T) -> io::Result<()> {
+        unsafe {
+            self.read_raw(offset, buf.buffer_len(), buf.buffer_mut_ptr())
+                .await
+        }
+    }
+
+    /// Reads data from the child node into a linear, potentially uninitialised typed buffer.
+    pub async fn read_uninit<T: SizedIoBuffer>(
+        &self,
+        offset: u64,
+        mut buf: MaybeUninit<T>,
+    ) -> io::Result<T> {
+        unsafe {
+            self.read_raw(offset, buf.buffer_len(), buf.buffer_mut_ptr())
+                .await?;
+            Ok(buf.assume_init())
+        }
+    }
+}
+
+#[doc(hidden)]
+pub unsafe extern "C" fn bdrv_open<D: BlockDriver>(
+    bs: *mut bindings::BlockDriverState,
+    options: *mut bindings::QDict,
+    _flags: std::os::raw::c_int,
+    errp: *mut *mut bindings::Error,
+) -> std::os::raw::c_int {
+    unsafe {
+        let v = match bindings::qobject_input_visitor_new_flat_confused(options, errp).as_mut() {
+            None => return -(bindings::EINVAL as std::os::raw::c_int),
+            Some(v) => v,
+        };
+
+        let mut opts: *mut D::Options = ptr::null_mut();
+        D::parse_options(v, &mut opts, errp);
+        bindings::visit_free(v);
+
+        let opts = match opts.as_mut() {
+            None => return -(bindings::EINVAL as std::os::raw::c_int),
+            Some(opts) => opts,
+        };
+
+        while let Some(e) = bindings::qdict_first(options).as_ref() {
+            bindings::qdict_del(options, e.key);
+        }
+
+        let ret = D::open(bs, opts, errp);
+        D::free_options(opts);
+        ret
+    }
+}
+
+#[doc(hidden)]
+pub unsafe extern "C" fn bdrv_close<D: BlockDriver>(bs: *mut bindings::BlockDriverState) {
+    unsafe {
+        let state = (*bs).opaque as *mut D;
+        ptr::drop_in_place(state);
+    }
+}
+
+/// Declare a format block driver. This macro is meant to be used at the top level.
+///
+/// `typ` is a type implementing the [`BlockDriver`] trait to handle the image format with the
+/// user-visible name `fmtname`.
+macro_rules! block_driver {
+    ($fmtname:expr, $typ:ty) => {
+        const _: () = {
+            static mut BLOCK_DRIVER: ::qemu_api::bindings::BlockDriver =
+                ::qemu_api::bindings::BlockDriver {
+                    format_name: ::qemu_api::c_str!($fmtname).as_ptr(),
+                    instance_size: ::std::mem::size_of::<$typ>() as i32,
+                    bdrv_open: Some($crate::driver::bdrv_open::<$typ>),
+                    bdrv_close: Some($crate::driver::bdrv_close::<$typ>),
+                    bdrv_child_perm: Some(::qemu_api::bindings::bdrv_default_perms),
+                    is_format: true,
+                    ..::qemu_api::zeroable::Zeroable::ZERO
+                };
+
+            qemu_api::module_init! {
+                MODULE_INIT_BLOCK => unsafe {
+                    ::qemu_api::bindings::bdrv_register(std::ptr::addr_of_mut!(BLOCK_DRIVER));
+                }
+            }
+        };
+    };
+}
+pub(crate) use block_driver;
diff --git a/rust/block/src/lib.rs b/rust/block/src/lib.rs
index 1c03549821..54ebd480ec 100644
--- a/rust/block/src/lib.rs
+++ b/rust/block/src/lib.rs
@@ -1,3 +1,4 @@
+mod driver;
 mod iobuffer;
 
 pub use iobuffer::{IoBuffer, SizedIoBuffer};
-- 
2.48.1